1. Field of the Invention
The present invention relates to an EGR device for use in an engine, and more specifically relates to a constructing technique for bypassing an EGR control valve equipped with the EGR device.
2. Related Art
Conventionally, there is widely known an EGR (Exhaust Gas Recirculation) device, which refluxes a part of exhaust gas from an exhaust system to an intake system in an engine, for the purpose of reducing nitrogen dioxide (Nox) generation included in the exhaust gas. There is also well known a technique of the EGR device for the engine provided with an EGR valve for controlling a reflux volume of the EGR gas, in the EGR device.
Meanwhile, because when an engine load is increased, the temperature of the exhaust gas (the EGR gas) is generally increased, there is widely known an EGR device provided with an EGR cooler near the EGR valve, so as to reflux the high-temperature EGR gas in a high load area, and there is well-known a technique for avoiding a damage of the EGR cooler and for enhancing the safety of the EGR device, by bypassing the EGR cooler and preventing an abnormal pressure increase of the EGR cooler.
For example, JP 2004-346918 discloses a technique, which a bypass passage bypassing the EGR cooler is connected between an EGR pipe upstream of the EGR gas and an EGR pipe downstream of the EGR gas in the EGR cooler, or between an EGR pipe upstream of the EGR gas and the engine intake system in the EGR cooler, as well as which a changeover valve is mounted to a bifurcated portion between the bypass passage and the EGR pipe upstream of the EGR gas, and a manometer is attached to the upstream of the EGR gas in the changeover valve and a thermometer is attached to a refrigerant lead-out port of the EGR cooler, wherein the control means bypasses the EGR gas to the bypass passage by controlling the opening and closing of the changeover valve, when any one of the detection values by the manometer or the thermometer reaches the predefined setting value.